1. Field of the Invention
The present invention relates to a control apparatus of a vibration type actuator, and in particular, to electronic apparatus such as a camera, observation equipment, and a lens apparatus that uses the vibration type actuator as a driving force.
2. Description of Related Art
In cameras and lens apparatuses, drive mechanisms each driving a lens with making a vibration type motor as a driving force may be adopted. This vibration type motor vibrates a vibration body by bonding an electro-mechanical energy converting element on a metallic elastic body and making it as a vibration body, and applying plural phases of frequency signals, whose phases are mutually different, to the electro-mechanical energy converting element. Then, this vibration type motor gets a driving force by relativity moving the vibration body and a contact body contacting with pressure to this vibration body (elastic body).
A practical system is one that controls the drive speed of a lens by changing a frequency of frequency signals inputted into an electro-mechanical energy converting element when a lens is driven by such a vibration type motor. In this system, since the drive speeds obtained by individual motors may be different, the frequency of frequency signals is often dealt as a relative value.
Then, quicker startup may be performed by storing the frequency of frequency signals at the time when the lens starts off every time the motor drives the lens and applying the frequency signals at the frequency, which is stored, when next starting the motor.
For example, Japanese Patent Publication No. H05(1993)-038553 discloses the technology of storing a frequency of frequency signals or a frequency within a predetermined range to this frequency at the time when detecting the start of relative drive of a movable body or an object of a vibration type motor, and using this value as an initial value at the next startup of the vibration type motor.
FIG. 8 shows the schematic structure of a focus lens drive system in a conventional lens apparatus.
The diagram shows a controller 210 controlling the operation of a lens drive system, a V-F converter 201 generating a frequency of a frequency signal to control the rotating speed (drive speed) of a vibration type motor 203, a drive circuit 202 that generates the frequency signal, having the frequency set by the V-F converter 201, and drives the vibration type motor 203, an encoder unit 204 to detect a drive amount and the drive speed of the vibration type motor 203, reduction gears 205 that decelerate an output of the vibration type motor 203 and transmits it to a focus lens 206, and an A/M switch 207 for selecting auto focus or manual focus so as to perform focusing.
Here, when the vibration type motor 203 is normally rotated, the focus lens 206 moves in the direction shown by an arrow X1 (direction of the optical axis) in FIG. 8. When reversely rotated, the focus lens 206 moves in the direction shown by an arrow X2 (direction of the optical axis).
FIG. 6 shows the relation between the frequency of frequency signals (drive signals) applied to the vibration type motor 203 and the rotating speed of the motor. In this graph, a range enclosed with a frame having reference numeral (4) is a frequency range of the drive signals used for driving the focus lens 206.
FIG. 7 shows the relation between the frequency of the drive signals and the drive speed of the vibration type motor 203 in a conventional lens drive system. An upper graph in FIG. 7 shows the change of the drive speed of the vibration type motor 203 to the drive time, and a lower graph shows the change of the frequency of the frequency signals, applied to the vibration type motor 203, to the drive time.
In FIG. 7, f1 denotes a starting-off frequency showing a frequency at the time when the vibration type motor 203 started off when being driven last time, that is, a frequency at the time when an output of the encoder 204 was started. In addition, f2 is a starting frequency at the time when being driven this time, and is set at the same frequency as the starting-off frequency f1 at the time when being driven last time, or a frequency that is higher by a predetermined frequency than the starting-off frequency f1. Then, when being driven this time, the vibration type motor 203 is accelerated by decreasing the frequency of the drive signals from the starting frequency f2.
By the way, reduction gears 205 are usually constituted of several steps of gear trains, screws, or the like so as to decelerate the rotating speed of the vibration type motor 203. Hence, when the vibration type motor 203 is driven in the reverse direction to the last driving, it becomes delayed to transmit power to the focus lens 206 by backlash in the reduction gears 205. Depending on the structure of the reduction gears 205, a backlash amount may become 20 to 30 pulses at the maximum by converting it into the output pulse count of the encoder 204.
Therefore, when reversely driving the vibration type motor 203, it is necessary to drive the vibration type motor 203 by the backlash in addition to the drive amount in the normal rotation (the same direction as that in the last driving) driving. Hence, as shown in FIG. 7, there is a problem that drive time in the reverse rotation (shown by a dotted line in this graph) becomes longer than that in the normal rotation (shown by a solid line in this graph) even if the drive amounts of the focus lens 206 are the same.